Name Date Period. 1. If drops of ACID are added to a ph buffer, then the ph of the buffer will [increase / decrease / stay the same].

Transcription

1 Name Date Period ACIDS AND BASES Organisms are often very sensitive to the effect of s and s in their environment. They need to maintain a stable internal ph in order to survive even in the event of environmental changes. Many naturally occurring biological, geological, and man-made chemicals are capable of stabilizing the environment s ph. This may allow organisms to better survive in diverse environments found throughout the earth. Teams will work in pairs, using one computer and two ph systems. One team will measure the effect of on biological materials, while the other team will measure the effect of on biological materials. Each group will test the biological materials assigned to them, and all groups will share their data at the end of the class. OBJECTIVES In this experiment, you will Add an to a material and note the extent that it resists changes in ph. Add a to a material and note the extent that it resists changes in ph. Work with classmates to compare the ability of different materials to resist ph changes. HYPOTHESIS 1. If drops of ACID are added to a ph buffer, then the ph of the buffer will [increase / decrease / stay the same]. 2. If drops of BASE are added to a ph buffer, then the ph of the buffer will [increase / decrease / stay the same]. MATERIALS INDIVIDUAL/TEAM MATERIALS: SHARED CLASS MATERIALS: - MacBook Air computer - 1 L 2% albumin (egg white) solution - LabQuest (Vernier computer interface) - 1 L 0.10 M bicarbonate solution - Logger Pro software - 1 L 0.10 M citric solution - 2 Vernier ph Sensors - various buffer solutions ml 0.10 M HCl () with dropper ml 0.10 M NaOH () with dropper - 2 stickers, labeled ACID and BASE ml flasks ml graduated cylinder ml beaker with water (HOH)

2 PROCEDURE 1. Obtain and wear goggles. Connect a Vernier ph probe into CH 1 and CH 2 of the LabQuest. 2. One person from each lab team will use the ph probe in CH 1. This probe will be used when adding ACID to the different solutions. The other person from each lab team will use the ph probe in CH 2. This probe will be used when adding BASE to the different solutions. Thoroughly rinse the two probes and place them into a 500 ml beaker that contains approximately 300 ml of water. Important: Do not let the ph electrodes dry out. Keep them in a 500 ml beaker with about 300 ml of tap water when not in use. The tip of the probe is made of glass it is fragile. Handle with care! 3. Connect the probes to the computer interface. Prepare the computer for data collection by opening the file 03 Acids and Bases from the Biology with Vernier folder of Logger Pro. Testing the effect of and on water 4. Label one of the 100 ml flasks ACID and label the other BASE. Place 30 ml of water in each flask. 5. On the data table, click on the labels ph 1 and ph 2. Change ph 1 to ACID and ph 2 to BASE. 6. Select Graph Options from the Options menu. First click on Axes Options. Label the Y-Axis ph of Water. Then click on Graph Options in the dialogue box that appears. Select the option that says Connect Points. Also select the option that says Legend. 7. Rinse the ph probe thoroughly with water. Then place it into the beaker to be tested: Person A: Place your probe in the beaker labeled ACID. Person B: Place your probe in the beaker labeled BASE. 8. Click to begin making ph measurements. 9. The group will be entering the number of drops of or added to the beaker. Before you begin, determine the initial ph of the solution. Click, then type 0 in the text box and press ENTER. 10. Add ACID or BASE to the solution. Stir each solution thoroughly after addition. CAUTION: Handle the hydrochloric with care. It can cause painful burns if it comes in contact with the skin. Sodium hydroxide solution is caustic. Avoid spilling it on your skin or clothing. Person A: Add 5 drops of to the beaker labeled ACID. Person B: Add 5 drops of to the beaker labeled BASE. 11. When the ph readings are stable click. Enter the total number of drops of or you have added to the water in the beaker. Type 5 in the text box and press ENTER. 12. Repeat Steps 10 11, adding 5 drops at a time until each person has added a total of 30 drops.

3 13. Click when you have added a total of 30 drops. 14. Select Print Graph from the File menu. Press OK when the Printing Options Desktop. Include your name(s) and WATER in the title. 15. Rinse the ph probe thoroughly and place the probe into the 500 ml beaker of tap water. Testing the effect of and on bicarbonate solution 16. Place 30 ml of bicarbonate solution in each beaker. 17. Select Graph Options from the Options menu. First click on Axes Options. Label the Y-Axis ph of Bicarbonate. Set the X-axis Scaling options for the graph to go from 0 to 100 drops. Then click on Graph Options in the dialogue box that appears. Select the option that says Connect Points. Also select the option that says Legend. 18. Click to begin making ph measurements. Select the option to Erase and 19. Repeat steps 9-12 for the bicarbonate solution, but add 10 drops of ACID or BASE at a time instead of 5 drops. Click when you have added a total of 100 drops. 20. Select Print Graph from the File menu. Press OK when the Printing Options Desktop. Include your name(s) and BICARBONATE in the title. 21. Rinse the ph probe thoroughly and place the probe into the 500 ml beaker of tap water. Testing the effect of and on a buffer solution 22. Place 30 ml of a buffer solution in each beaker. Record the ph of the buffer solution that you chose. 23. Select Graph Options from the Options menu. First click on Axes Options. Label the Y-Axis ph of Buffer Solution. Set the X-axis Scaling options for the graph to go from 0 to 100 drops. Then click on Graph Options in the dialogue box that appears. Select the option that says Connect Points. Also select the option that says Legend. 24. Click to begin making ph measurements. Select the option to Erase and 25. Repeat steps 9-12 for the buffer solution, but add 10 drops of ACID or BASE at a time instead of 5 drops. Click when you have added a total of 100 drops. 26. Select Print Graph from the File menu. Press OK when the Printing Options Desktop. Include your name(s) and BUFFER in the title. 27. Rinse the ph probe thoroughly and place the probe into the 500 ml beaker of tap water.

4 Testing the effect of and on citric solution 28. Place 30 ml of citric solution in each beaker. 29. Select Graph Options from the Options menu. First click on Axes Options. Label the Y-Axis ph of Citric Acid. Set the X-axis Scaling options for the graph to go from 0 to 30 drops. Then click on Graph Options in the dialogue box that appears. Select the option that says Connect Points. Also select the option that says Legend. 30. Click to begin making ph measurements. Select the option to Erase and 31. Repeat steps 9-12 for the citric solution. Remember to add 5 drops of ACID or BASE at a time. Click when you have added a total of 30 drops. 32. Select Print Graph from the File menu. Press OK when the Printing Options Desktop. Include your name(s) and CITRIC ACID in the title. 33. Rinse the ph probe thoroughly and place the probe into the 500 ml beaker of tap water. Testing the effect of and on albumin (egg white) solution 34. Place 30 ml of albumin (egg white) solution in each beaker. 35. Select Graph Options from the Options menu. First click on Axes Options. Label the Y-Axis ph of Albumin. Set the X-axis Scaling options for the graph to go from 0 to 100 drops. Then click on Graph Options in the dialogue box that appears. Select the option that says Connect Points. Also select the option that says Legend. 36. Click to begin making ph measurements. Select the option to Erase and 37. Repeat steps 9-12 for the albumin solution, but add 10 drops of ACID or BASE at a time instead of 5 drops. Click when you have added a total of 100 drops. 38. Select Print Graph from the File menu. Press OK when the Printing Options Desktop. Include your name(s) and ALBUMIN in the title. 39. Rinse the ph probe thoroughly and place the probe into the 500 ml beaker of tap water. NOTES REGARDING DATA TABLES 1. The Greek symbol Δ refers to the change in something. Mathematically, it means to calculate the difference by subtracting the initial value from the final value. 2. The Total Buffer Range refers to the range of drops in which the ph level generally stays the same. 3. Your lab report will contain 10 data tables. For each section of this experiment, you will need to include a data table as well as a graph. You will be permitted to cut out or scan data tables 1, 3, 5, 7, and 9 and to paste/insert them into your lab report. 4. If you are unable to print your graphs in color, you are required to indicate which line represents drops of and which line represents drops of. You should trace the lines using colored pencils and make sure that a legend is included.

5 RESULTS Data Table #1: ΔpH Buffer ph (if any) Water Data Table #2: (Attach a graph that displays the information from Data Table #1.) Data Table #3: ΔpH Buffer ph (if any) Bicarbonate Data Table #4: (Attach a graph that displays the information from Data Table #3.) Data Table #5: ΔpH Buffer ph (if any) ph Buffer Data Table #6: (Attach a graph that displays the information from Data Table #5.)

6 Data Table #7: ΔpH Buffer ph (if any) Citric Acid Data Table #8: (Attach a graph that displays the information from Data Table #7.) Data Table #9: ΔpH Buffer ph (if any) Albumin Data Table #10: (Attach a graph that displays the information from Data Table #9.) PROCESSING THE DATA 1. How should the ph of a material to test in the ACID beaker compare to that in the BASE beaker before any or is added? Why? 2. What was the purpose of collecting the information in data table #1? 3. Generally, what was the effect of adding HCl to each solution? Was this true for every solution? Why do you think this happened the way it did? 4. Generally, what was the effect of adding NaOH to each solution? Was this true for every solution? Why do you think this happened the way it did? 5. What was the effect of adding HCl or NaOH to the buffer solution? Explain using CLAIM à EVIDENCE à REASONING. 6. Which of the first four solutions acted the most like a buffer solution? Explain using CLAIM à EVIDENCE à REASONING. 7. What is the name of the chemical used to buffer blood in most mammals, including humans? Why do you think this chemical is necessary?